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Abstract:

A measurement system measures a parameter of a muscular-skeletal system.
The measurement system is placed in proximity to the muscular-skeletal
system such that the parameter to be measured is applied to a sensing
assemblage (3). The measurement system further comprises a digital
counter (20), a digital timer (22), a digital clock 24, and a data
register (26). The digital counter (20) is preset to a predetermined
number of measurement cycles. The digital timer (22) measures an elapsed
time of a measurement sequence comprising the predetermined number of
measurement cycles. The digital counter (20) is decremented each
measurement cycle until a zero count is reached thereby stopping the
measurement sequence. The digital timer (22) measures an elapsed time of
the measurement sequence. The parameter value can be related to the
elapsed time. The precision of a parameter measurement can be modified by
changing the predetermined number of measurement cycles.

Claims:

1. A high precision method to measure a parameter corresponding to the
muscular-skeletal system comprising the steps of:presetting a measurement
sequence for a predetermined number of measurement cycles;generating a
sum corresponding to the measurement sequence; andmeasuring an elapsed
time of the measurement sequence.

2. The method of claim 1 further including a step of increasing the
predetermined number of measurement cycles to raise measurement
precision.

3. The method of claim 1 further including a step of dividing the sum
corresponding to the measurement sequence by the elapsed time.

4. The method of claim 3 further including the steps of:applying the
parameter to a medium during the measurement sequence;emitting an energy
wave into the medium;detecting a propagated energy wave;counting each
detected propagated energy wave; andstopping the measurement sequence
when a count of detected propagated energy waves equals the predetermined
number of measurement cycles.

5. The method of claim 4 further including a step of emitting an energy
wave into the medium upon detection of each propagated energy wave to
sustain energy wave propagation during the measurement sequence.

6. The method of claim 5 further including a step of maintaining an
integer number of energy waves in the medium during the measurement
sequence.

7. The method of claim 5 further including a step of relating a transit
time, frequency, or phase measured during the measurement sequence to
generate a parameter measurement.

8. The method of claim 1 further including the steps of:setting a counter
to the predetermined number of measurement cycles;decrementing the
counter upon detection of each propagated energy wave; andstopping the
measurement sequence when the counter decrements to zero.

9. The method of claim 8 further including the steps of:dividing the
predetermined number of measurement cycles by the elapsed time;
andstoring a result in a data register.

10. The method of claim 9 further including the steps of:placing a sensing
module in proximity to the muscular-skeletal system such that the
parameter to be measured is applied directly or indirectly to the sensing
module; andcontrolling an operation of the sensing module wirelessly to
achieve a specific resolution of measurement data; control processes that
include adjusting an ultrasonic frequency, a sampling frequency, a
waveguide length, a data rate, and bandwidth in real-time.

11. A method of measuring a parameter of the muscular-skeletal system
comprising the steps of:placing a sensing assemblage in proximity to the
muscular-skeletal system;setting a precision level and resolution of
captured data to optimize a trade-off between measurement resolution
versus ultrasonic frequency prior to a measurement sequence; andadjusting
a bandwidth of a transceiver providing data communications to deliver the
captured data in real-time.

12. The method of claim 11, further including a step of optimizing the
tradeoff by evaluating measurement resolution versus a length of a
waveguide propagation medium;

13. The method of claim 11 further including a step of optimizing the
tradeoff by adjusting the frequency of the ultrasonic energy waves or
repetition rate or energy pulses;

14. The method of claim 11 further including a step of optimizing the
tradeoff by adjusting a bandwidth of sensing and data capture operations.

15. The method of claim 11, comprising accumulating multiple cycles of
excitation and transit time of ultrasonic energy waves.

16. The method of claim 11, comprising controlling a digital counter to
run through multiple measurement cycles, each cycle having excitation and
transit phases such that there is not lag between successive measurement
cycles, and capturing a total elapsed time.

17. A measurement system to measure a parameter of the muscular-skeletal
system comprising:a sensor placed in proximity to the muscular-skeletal
system;a digital counter coupled to a sensor where a signal corresponding
to a measurement cycle of the sensor clocks the digital counter;a digital
timer to measure an elapsed time of a measurement sequence where the
measurement sequence comprises a predetermined number of measurement
cycles;a data register coupled to the digital timer to store a number
calculated from the predetermined number of measurement cycles and the
elapsed time of the measurement sequence.

18. The measurement system of claim 17 where the precision of a parameter
measurement increases by increasing the predetermined number of
measurement cycles.

19. The measurement system of claim 18 further including a clock
operatively coupled to the digital counter and the digital timer where a
parameter value relates to a time period of a measurement cycle and where
the digital timer elapsed time is a sum of individual parameter
measurements.

20. The measurement system of claim 19 where the measurement system
comprises one or more sensing assemblies, one or more load surfaces, an
accelerometer, electronic circuitry, a transceiver, and an energy supply,
where the measurement system measures forces, such as an applied load,
and transmits the measurement data to a secondary system for further
processing and display.

[0002]The present invention pertains generally to measurement of physical
parameters, and particularly to, but not exclusively, to electronic
devices and signal processing techniques for high precision sensing at
optimal operating points.

BACKGROUND

[0003]The skeletal system of a mammal is subject to variations among
species. Further changes can occur due to environmental factors,
degradation through use, and aging. An orthopedic joint of the skeletal
system typically comprises two or more bones that move in relation to one
another. Movement is enabled by muscle tissue and tendons attached to the
skeletal system of the joint. Ligaments hold and stabilize the one or
more joint bones positionally. Cartilage is a wear surface that prevents
bone-to-bone contact, distributes load, and lowers friction.

[0004]There has been substantial growth in the repair of the human
skeletal system. In general, orthopedic joints have evolved as
information from simulations, mechanical prototypes, and long-term
patient joint replacement data is collected and used to initiate improved
designs. Similarly, the tools being used for orthopedic surgery have been
refined over the years but have not changed substantially. Thus, the
basic procedure for replacement of an orthopedic joint has been
standardized to meet the general needs of a wide distribution of the
population. Although the tools, procedure, and artificial joint meet a
general need, each replacement procedure is subject to significant
variation from patient to patient. The correction of these individual
variations relies on the skill of the surgeon to adapt and fit the
replacement joint using the available tools to the specific circumstance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005]Various features of the system are set forth with particularity in
the appended claims. The embodiments herein, can be understood by
reference to the following description, taken in conjunction with the
accompanying drawings, in which:

[0006]FIG. 1 is an exemplary block diagram of a propagation tuned
oscillator (PTO) to maintain positive closed-loop feedback in accordance
with an exemplary embodiment;

[0007]FIG. 2 is a simplified cross-sectional view of a sensing module in
accordance with an exemplary embodiment;

[0008]FIG. 3 is an exemplary assemblage for illustrating reflectance and
unidirectional modes of operation in accordance with an exemplary
embodiment;

[0009]FIG. 4 is an exemplary assemblage that illustrates propagation of
ultrasound waves within a waveguide in the bi-directional mode of
operation of this assemblage;

[0010]FIG. 5 is an exemplary cross-sectional view of a sensor element to
illustrate changes in the propagation of ultrasound waves with changes in
the length of a waveguide;

[0011]FIG. 6 is a simplified flow chart of method steps for high precision
processing and measurement data in accordance with an exemplary
embodiment; and

[0012]FIG. 7 is an illustration of a sensor placed in contact between a
femur and a tibia for measuring a parameter in accordance with an
exemplary embodiment.

DETAILED DESCRIPTION

[0013]Embodiments of the invention are broadly directed to measurement of
physical parameters, and more particularly, to a method for analyzing
measurement data that achieves accurate, repeatable, high precision and
high-resolution measurements. The system disclosed herein relates to
real-time measurement of load, force, pressure, displacement, density,
viscosity, or localized temperature by a sensor. In one embodiment, the
method includes evaluating changes in a transit time of energy pulses or
propagating waves within elastic energy propagating structures as a
function of an operating point and controlling the resolution of
measurements of the changes in this transit time to achieve optimal
operating point conditions.

[0014]In a first embodiment, a wireless sensing module comprises one or
more sensing assemblies, one or more load surfaces, an accelerometer,
electronic circuitry, a transceiver, and an energy supply. The wireless
sensing module measures a parameter applied to the sensing module. In one
embodiment, the wireless sensing module measures force, such as an
applied load, and transmit the measurement data to a secondary system for
further processing and display. For example, the wireless sensing module
can be used for intra-operative sensing of a joint implant during surgery
to the muscular-skeletal system or as a long term implanted sensor in an
artificial joint or implanted in the natural muscular-skeletal system. In
the example, the electronic circuitry in conjunction with the sensing
assemblies accurately measures physical displacements of the load
surfaces on the order of a few microns along various physical dimensions.
It does this by evaluating propagation characteristics of ultrasonic
energy waves in one or more waveguides of the sensing assemblies that
physically change in response to the applied forces. In particular, it
measures changes in propagation time due to changes in the length of the
waveguides; physical length changes which occur in direct response to the
applied force.

[0015]A method disclosed herein includes setting the precision level and
resolution of captured data to optimize a trade-off between measurement
resolution versus real-time operation. In one embodiment, the measurement
resolution is adjusted corresponding to the ultrasonic frequency of the
sensor. This can further include modifying the bandwidth of the
transceiver providing data communications that deliver the data in
real-time. For instance, by way of example, the wireless sensing module
over-samples data measurements through a series of repeated measurements
based on the ultrasonic frequency, accumulates the over-sampled data
specific to achieving a numerical dynamic range, estimates a single data
measurement from the over-sampled data, and determines if the precision
of the single data measurement for a given bandwidth is achieved at an
optimal operating point, and furthermore without compromising resolution
of the measurements.

[0016]More specifically, in this embodiment, the electronic circuitry is
designed, or programmed, to evaluate tradeoffs between i) measurement
resolution versus length of the waveguide propagation medium, ii)
frequency of the ultrasonic energy waves or repetition rate or energy
pulses, and iii) bandwidth of the sensing and data capture operations. In
view of the tradeoffs, the system controls the operation of the wireless
sensing module to achieve a specific resolution of measurement data and
controls processes which include adjusting the ultrasonic frequency,
sampling frequency, data rate and bandwidth in real-time. For instance,
by way of example, the wireless sensing module can increase the sampling
rate, increase the ultrasonic frequency, and increase the data rate as an
applied load further displaces a load surface along a graded displacement
curve (e.g., predetermined threshold levels).

[0017]In one embodiment, the method can include accumulating multiple
cycles of excitation and transit time of ultrasonic energy waves. This
improves the level of resolution of measurement of changes in length or
other aspect of the elastic energy propagating structure instead of
averaging transit time of multiple individual excitation and transit
cycles. In particular, the electronic circuitry controls a digital
counter to run through multiple measurement cycles, each cycle having
excitation and transit phases such that there is not lag between
successive measurement cycles, and capture the total elapsed time. The
digital counter can be set to achieve a specific numerical dynamic range,
for instance, as a user adjustable parameter.

[0018]This method for analyzing measurement data can be applied generally
to real-time measurement of the muscular-skeletal system. Disclosed
hereinbelow, an analysis is performed on data generated by elastic energy
propagating structures or media of a wide range of lengths as required by
the application, including compact elastic energy propagating structures
or media on the order of a millimeter to elastic energy propagating
structures or media that are orders of magnitude longer. Submicron
resolution is achieved over this broad range of lengths of elastic energy
propagating structures or media, when operated in conjunction with data
capture and processing circuitry implementing this method of capturing
and analyzing measurement data.

[0019]In one embodiment, a propagation tuned oscillator (PTO) is provided
to maintain positive closed-loop feedback of energy waves in one or more
energy propagating structures of a sensing system. The energy waves
propagate through a medium in an energy propagating structure. A positive
feedback closed-loop circuit causes the oscillator to tune the resonant
frequency of the energy waves in accordance with physical changes in the
one or more energy propagating structures; hence the term, propagation
tuned oscillator. Detection of a propagated energy wave through at least
a portion of the medium is detected by the PTO. The detection of the
propagated energy wave initiates an energy wave emission into the medium
thereby sustaining a process by which energy waves continually propagate
through the medium.

[0020]In general, the PTO is used to measure a parameter. The parameter is
applied to the medium of the energy propagating structure. The parameter
causes a physical change in the medium. In one embodiment, the physical
change is a dimensional change such as a change in length resulting from
externally applied forces or pressure. The physical changes in the energy
propagating structures change in direct proportion to the external
applied forces and can be precisely evaluated to measure the applied
forces.

[0021]FIG. 1 is an exemplary block diagram 100 of a propagation tuned
oscillator (PTO) 4 to maintain positive closed-loop feedback in
accordance with an exemplary embodiment. The measurement system includes
a sensing assemblage 1 and propagation tuned oscillator (PTO) 4 that
detects energy waves 2 in one or more waveguides 3 of the sensing
assemblage 1. In one embodiment, energy waves 2 are ultrasound waves. A
pulse 11 is generated in response to the detection of energy waves 2 to
initiate a propagation of a new energy wave in waveguide 3. It should be
noted that ultrasound energy pulses or waves, the emission of ultrasound
pulses or waves by ultrasound resonators or transducers, transmitted
through ultrasound waveguides, and detected by ultrasound resonators or
transducers are used merely as examples of energy pulses, waves, and
propagation structures and media. Other embodiments herein contemplated
can utilize other wave forms, such as, light.

[0022]The sensing assemblage 1 comprises transducer 5, transducer 6, and a
waveguide 3 (or energy propagating structure). In a non-limiting example,
sensing assemblage 1 is affixed to load bearing or contacting surfaces 8.
External forces applied to the contacting surfaces 8 compress the
waveguide 3 and change the length of the waveguide 3. Under compression,
transducers 5 and 6 will also be moved closer together. The change in
distance affects the transit time 7 of energy waves 2 transmitted and
received between transducers 5 and 6. The propagation tuned oscillator 4
in response to these physical changes will detect each energy wave sooner
(e.g. shorter transit time) and initiate the propagation of new energy
waves associated with the shorter transit time. As will be explained
below, this is accomplished by way of PTO 4 in conjunction with the pulse
generator 10, the mode control 12, and the phase detector 14.

[0023]Notably, changes in the waveguide 3 (energy propagating structure or
structures) alter the propagation properties of the medium of propagation
(e.g. transit time 7). The energy wave can be a continuous wave or a
pulsed energy wave. A pulsed energy wave approach reduces power
dissipation allowing for a temporary power source such as a battery or
capacitor to power the system during the course of operation. In at least
one exemplary embodiment, a continuous wave energy wave or a pulsed
energy wave is provided by transducer 5 to a first surface of waveguide
3. Transducer 5 generates energy waves 2 that are coupled into waveguide
3. In a non-limiting example, transducer 5 is a piezo-electric device
capable of transmitting and receiving acoustic signals in the ultrasonic
frequency range.

[0024]Transducer 6 is coupled to a second surface of waveguide 3 to
receive the propagated pulsed signal and generates a corresponding
electrical signal. The electrical signal output by transducer 6 is
coupled to phase detector 14. In general, phase detector 14 compares the
timing of a selected point on the waveform of the detected energy wave
with respect to the timing of the same point on the waveform of other
propagated energy waves. In a first embodiment, phase detector 14 can be
a zero-crossing receiver. In a second embodiment, phase detector 14 can
be an edge-detect receiver. In the example where sensing assemblage 1 is
compressed, the detection of the propagated energy waves 2 occurs earlier
(due to the length/distance reduction of waveguide 3) than a signal prior
to external forces being applied to contacting surfaces. Pulse generator
10 generates a new pulse in response to detection of the propagated
energy waves 2 by phase detector 14. The new pulse is provided to
transducer 5 to initiate a new energy wave sequence. Thus, each energy
wave sequence is an individual event of energy wave propagation, energy
wave detection, and energy wave emission that maintains energy waves 2
propagating in waveguide 3.

[0025]The transit time 7 of a propagated energy wave is the time it takes
an energy wave to propagate from the first surface of waveguide 3 to the
second surface. There is delay associated with each circuit described
above. Typically, the total delay of the circuitry is significantly less
than the propagation time of an energy wave through waveguide 3. In
addition, under equilibrium conditions variations in circuit delay are
minimal. Multiple pulse to pulse timings can be used to generate an
average time period when change in external forces occur relatively
slowly in relation to the pulsed signal propagation time such as in a
physiologic or mechanical system. The digital counter 20 in conjunction
with electronic components counts the number of propagated energy waves
to determine a corresponding change in the length of the waveguide 3.
These changes in length change in direct proportion to the external force
thus enabling the conversion of changes in parameter or parameters of
interest into electrical signals.

[0026]The block diagram 100 further includes counting and timing
circuitry. More specifically, the timing, counting, and clock circuitry
comprises a digital timer 20, a digital timer 22, a digital clock 24, and
a data register 26. The digital clock 24 provides a clock signal to
digital counter 20 and digital timer 22 during a measurement sequence.
The digital counter 20 is coupled to the propagation tuned oscillator 4.
Digital timer 22 is coupled to data register 26. Digital timer 20,
digital timer, 22, digital clock 24 and data register 26 capture transit
time 7 of energy waves 2 emitted by ultrasound resonator or transducer 5,
propagated through waveguide 3, and detected by or ultrasound resonator
or transducer 5 or 6 depending on the mode of the measurement of the
physical parameters of interest applied to surfaces 8. The operation of
the timing and counting circuitry is disclosed in more detail
hereinbelow.

[0027]The measurement data can be analyzed to achieve accurate,
repeatable, high precision and high resolution measurements. This method
enables the setting of the level of precision or resolution of captured
data to optimize trade-offs between measurement resolution versus
frequency, including the bandwidth of the sensing and data processing
operations, thus enabling a sensing module or device to operate at its
optimal operating point without compromising resolution of the
measurements. This is achieved by the accumulation of multiple cycles of
excitation and transit time instead of averaging transit time of multiple
individual excitation and transit cycles. The result is accurate,
repeatable, high precision and high resolution measurements of parameters
of interest in physical systems.

[0028]In at least one exemplary embodiment, propagation tuned oscillator 4
in conjunction with one or more sensing assemblages 1 are used to take
measurements on a muscular-skeletal system. In a non-limiting example,
sensing assemblage 1 is placed between a femoral prosthetic component and
tibial prosthetic component to provide measured load information that
aids in the installation of an artificial knee joint. Sensing assemblage
1 can also be a permanent component or a muscular-skeletal joint or
artificial muscular-skeletal joint to monitor joint function. The
measurements can be made in extension and in flexion. In the example,
assemblage 1 is used to measure the condyle loading to determine if it
falls within a predetermined range and location. Based on the
measurement, the surgeon can select the thickness of the insert such that
the measured loading and incidence with the final insert in place will
fall within the predetermined range. Soft tissue tensioning can be used
by a surgeon to further optimize the force or pressure. Similarly, two
assemblages 1 can be used to measure both condyles simultaneously or
multiplexed. The difference in loading (e.g. balance) between condyles
can be measured. Soft tissue tensioning can be used to reduce the force
on the condyle having the higher measured loading to reduce the measured
pressure difference between condyles.

[0029]One method of operation holds the number of energy waves propagating
through waveguide 3 as a constant integer number. A time period of an
energy wave corresponds to energy wave periodicity. A stable time period
is one in which the time period changes very little over a number of
energy waves. This occurs when conditions that affect sensing assemblage
1 stay consistent or constant. Holding the number of energy waves
propagating through waveguide 3 to an integer number is a constraint that
forces a change in the time between pulses when the length of waveguide 3
changes. The resulting change in time period of each energy wave
corresponds to a change in aggregate energy wave time period that is
captured using digital counter 20 as a measurement of changes in external
forces or conditions applied to contacting surfaces 8.

[0030]A further method of operation according to one embodiment is
described hereinbelow for energy waves 2 propagating from transducer 5
and received by transducer 6. In at least one exemplary embodiment,
energy waves 2 is an ultrasonic energy wave. Transducers 5 and 6 are
piezo-electric resonator transducers. Although not described, wave
propagation can occur in the opposite direction being initiated by
transducer 6 and received by transducer 5. Furthermore, detecting
ultrasound resonator transducer 6 can be a separate ultrasound resonator
as shown or transducer 5 can be used solely depending on the selected
mode of propagation (e.g. reflective sensing). Changes in external forces
or conditions applied to contacting surfaces 8 affect the propagation
characteristics of waveguide 3 and alter transit time 7. As mentioned
previously, propagation tuned oscillator 4 holds constant an integer
number of energy waves 2 propagating through waveguide 3 (e.g. an integer
number of pulsed energy wave time periods) thereby controlling the
repetition rate. As noted above, once PTO 4 stabilizes, the digital
counter 20 digitizes the repetition rate of pulsed energy waves, for
example, by way of edge-detection, as will be explained hereinbelow in
more detail.

[0031]In an alternate embodiment, the repetition rate of pulsed energy
waves 2 emitted by transducer 5 can be controlled by pulse generator 10.
The operation remains similar where the parameter to be measured
corresponds to the measurement of the transit time 7 of pulsed energy
waves 2 within waveguide 3. It should be noted that an individual
ultrasonic pulse can comprise one or more energy waves with a damping
wave shape. The energy wave shape is determined by the electrical and
mechanical parameters of pulse generator 10, interface material or
materials, where required, and ultrasound resonator or transducer 5. The
frequency of the energy waves within individual pulses is determined by
the response of the emitting ultrasound resonator 4 to excitation by an
electrical pulse 11. The mode of the propagation of the pulsed energy
waves 2 through waveguide 3 is controlled by mode control circuitry 12
(e.g., reflectance or uni-directional). The detecting ultrasound
resonator or transducer may either be a separate ultrasound resonator or
transducer 6 or the emitting resonator or transducer 5 depending on the
selected mode of propagation (reflectance or unidirectional).

[0032]In general, accurate measurement of physical parameters is achieved
at an equilibrium point having the property that an integer number of
pulses are propagating through the energy propagating structure at any
point in time. Measurement of changes in the "time-of-flight" or transit
time of ultrasound energy waves within a waveguide of known length can be
achieved by modulating the repetition rate of the ultrasound energy waves
as a function of changes in distance or velocity through the medium of
propagation, or a combination of changes in distance and velocity, caused
by changes in the parameter or parameters of interest.

[0033]It should be noted that ultrasound energy pulses or waves, the
emission of ultrasound pulses or waves by ultrasound resonators or
transducers, transmitted through ultrasound waveguides, and detected by
ultrasound resonators or transducers are used merely as examples of
energy pulses, waves, and propagation structures and media. Other
embodiments herein contemplated can utilize other wave forms, such as,
light. Furthermore, the velocity of ultrasound waves within a medium may
be higher than in air. With the present dimensions of the initial
embodiment of a propagation tuned oscillator the waveguide is
approximately three wavelengths long at the frequency of operation.

[0034]Measurement by propagation tuned oscillator 4 and sensing assemblage
1 enables high sensitivity and high signal-to-noise ratio. The time-based
measurements are largely insensitive to most sources of error that may
influence voltage or current driven sensing methods and devices. The
resulting changes in the transit time of operation correspond to
frequency, which can be measured rapidly, and with high resolution. This
achieves the required measurement accuracy and precision thus capturing
changes in the physical parameters of interest and enabling analysis of
their dynamic and static behavior.

[0035]These measurements may be implemented with an integrated wireless
sensing module or device having an encapsulating structure that supports
sensors and load bearing or contacting surfaces and an electronic
assemblage that integrates a power supply, sensing elements, energy
transducer or transducers and elastic energy propagating structure or
structures, biasing spring or springs or other form of elastic members,
an accelerometer, antennas and electronic circuitry that processes
measurement data as well as controls all operations of ultrasound
generation, propagation, and detection and wireless communications. The
electronics assemblage also supports testability and calibration features
that assure the quality, accuracy, and reliability of the completed
wireless sensing module or device.

[0036]The level of accuracy and resolution achieved by the integration of
energy transducers and an energy propagating structure or structures
coupled with the electronic components of the propagation tuned
oscillator enables the construction of, but is not limited to, compact
ultra low power modules or devices for monitoring or measuring the
parameters of interest. The flexibility to construct sensing modules or
devices over a wide range of sizes enables sensing modules to be tailored
to fit a wide range of applications such that the sensing module or
device may be engaged with, or placed, attached, or affixed to, on, or
within a body, instrument, appliance, vehicle, equipment, or other
physical system and monitor or collect data on physical parameters of
interest without disturbing the operation of the body, instrument,
appliance, vehicle, equipment, or physical system.

[0037]FIG. 2 is a simplified cross-sectional view of a sensing module 101
in accordance with an exemplary embodiment. The sensing module (or
assemblage) is an electro-mechanical assembly comprising electrical
components and mechanical components that when configured and operated in
accordance with a sensing mode performs as a positive feedback
closed-loop measurement system. The measurement system can precisely
measure applied forces, such as loading, on the electro-mechanical
assembly. The sensing mode can be a continuous mode, a pulse mode, or a
pulse echo-mode.

[0038]In one embodiment, the electrical components can include ultrasound
resonators or transducers, ultrasound waveguides, and signal processing
electronics, but are not limited to these. The mechanical components can
include biasing springs 32, spring retainers and posts, and load
platforms 6, but are not limited to these. The electrical components and
mechanical components can be inter-assembled (or integrated) onto a
printed circuit board 36 to operate as a coherent ultrasonic measurement
system within sensing module 101 and according to the sensing mode. As
will be explained ahead in more detail, the signal processing electronics
incorporate a propagation tuned oscillator (PTO) or a phase locked loop
(PLL) to control the operating frequency of the ultrasound resonators or
transducers for providing high precision sensing. Furthermore, the signal
processing electronics incorporate detect circuitry that consistently
detects an energy wave after it has propagated through a medium. The
detection initiates the generation of a new energy wave by an ultrasound
resonator or transducer that is coupled to the medium for propagation
therethrough. A change in transit time of an energy wave through the
medium is measured and correlates to a change in material property of the
medium due to one or more parameters applied thereto.

[0039]Sensing module 101 comprises one or more assemblages 1 each
comprised one or more ultrasound resonators. As illustrated, waveguide 3
is coupled between transducers 5 and 6 and affixed to load bearing or
contacting surfaces 8. In one exemplary embodiment, an ultrasound signal
is coupled for propagation through waveguide 3. The sensing module 101 is
placed, attached to, or affixed to, or within a body, instrument, or
other physical system 18 having a member or members 16 in contact with
the load bearing or contacting surfaces 8 of the sensing module 101. This
arrangement facilitates translating the parameters of interest into
changes in the length or compression or extension of the waveguide or
waveguides 3 within the sensing module 101 and converting these changes
in length into electrical signals. This facilitates capturing data,
measuring parameters of interest and digitizing that data, and then
subsequently communicating that data through antenna 34 to external
equipment with minimal disturbance to the operation of the body,
instrument, appliance, vehicle, equipment, or physical system 18 for a
wide range of applications.

[0040]The sensing module 101 supports three modes of operation of energy
wave propagation and measurement: reflectance, unidirectional, and
bi-directional. These modes can be used as appropriate for each
individual application. In unidirectional and bi-directional modes, a
chosen ultrasound resonator or transducer is controlled to emit pulses of
ultrasound waves into the ultrasound waveguide and one or more other
ultrasound resonators or transducers are controlled to detect the
propagation of the pulses of ultrasound waves at a specified location or
locations within the ultrasound waveguide. In reflectance or pulse-echo
mode, a single ultrasound or transducer emits pulses of ultrasound waves
into waveguide 3 and subsequently detects pulses of echo waves after
reflection from a selected feature or termination of the waveguide. In
pulse-echo mode, echoes of the pulses can be detected by controlling the
actions of the emitting ultrasound resonator or transducer to alternate
between emitting and detecting modes of operation. Pulse and pulse-echo
modes of operation may require operation with more than one pulsed energy
wave propagating within the waveguide at equilibrium.

[0041]Many parameters of interest within physical systems or bodies can be
measured by evaluating changes in the transit time of energy pulses. The
frequency, as defined by the reciprocal of the average period of a
continuous or discontinuous signal, and type of the energy pulse is
determined by factors such as distance of measurement, medium in which
the signal travels, accuracy required by the measurement, precision
required by the measurement, form factor of that will function with the
system, power constraints, and cost. The physical parameter or parameters
of interest can include, but are not limited to, measurement of load,
force, pressure, displacement, density, viscosity, localized temperature.
These parameters can be evaluated by measuring changes in the propagation
time of energy pulses or waves relative to orientation, alignment,
direction, or position as well as movement, rotation, or acceleration
along an axis or combination of axes by wireless sensing modules or
devices positioned on or within a body, instrument, appliance, vehicle,
equipment, or other physical system.

[0042]In the non-limiting example, pulses of ultrasound energy provide
accurate markers for measuring transit time of the pulses within
waveguide 3. In general, an ultrasonic signal is an acoustic signal
having a frequency above the human hearing range (e.g. >20 KHz)
including frequencies well into the megahertz range. In one embodiment, a
change in transit time of an ultrasonic energy pulse corresponds to a
difference in the physical dimension of the waveguide from a previous
state. For example, a force or pressure applied across the knee joint
compresses waveguide 3 to a new length and changes the transit time of
the energy pulse When integrated as a sensing module and inserted or
coupled to a physical system or body, these changes are directly
correlated to the physical changes on the system or body and can be
readily measured as a pressure or a force.

[0043]FIG. 3 is an exemplary assemblage 200 for illustrating reflectance
and unidirectional modes of operation in accordance with an exemplary
embodiment. It comprises one or more transducers 202, 204, and 206, one
or more waveguides 214, and one or more optional reflecting surfaces 216.
The assemblage 200 illustrates propagation of ultrasound waves 218 within
the waveguide 214 in the reflectance and unidirectional modes of
operation. Either ultrasound resonator or transducer 202 and 204 in
combination with interfacing material or materials 208 and 210, if
required, can be selected to emit ultrasound waves 218 into the waveguide
214.

[0044]In unidirectional mode, either of the ultrasound resonators or
transducers for example 202 can be enabled to emit ultrasound waves 218
into the waveguide 214. The non-emitting ultrasound resonator or
transducer 204 is enabled to detect the ultrasound waves 218 emitted by
the ultrasound resonator or transducer 202.

[0045]In reflectance mode, the ultrasound waves 218 are detected by the
emitting ultrasound resonator or transducer 202 after reflecting from a
surface, interface, or body at the opposite end of the waveguide 214. In
this mode, either of the ultrasound resonators or transducers 202 or 204
can be selected to emit and detect ultrasound waves. Additional
reflection features 216 can be added within the waveguide structure to
reflect ultrasound waves. This can support operation in a combination of
unidirectional and reflectance modes. In this mode of operation, one of
the ultrasound resonators, for example resonator 202 is controlled to
emit ultrasound waves 218 into the waveguide 214. Another ultrasound
resonator or transducer 206 is controlled to detect the ultrasound waves
218 emitted by the emitting ultrasound resonator 202 (or transducer)
subsequent to their reflection by reflecting feature 216.

[0046]FIG. 4 is an exemplary assemblage 300 that illustrates propagation
of ultrasound waves 310 within the waveguide 306 in the bi-directional
mode of operation of this assemblage. In this mode, the selection of the
roles of the two individual ultrasound resonators (302, 304) or
transducers affixed to interfacing material 320 and 322, if required, are
periodically reversed. In the bi-directional mode the transit time of
ultrasound waves propagating in either direction within the waveguide 306
can be measured. This can enable adjustment for Doppler effects in
applications where the sensing module 308 is operating while in motion
316. Furthermore, this mode of operation helps assure accurate
measurement of the applied load, force, pressure, or displacement by
capturing data for computing adjustments to offset this external motion
316. An advantage is provided in situations wherein the body, instrument,
appliance, vehicle, equipment, or other physical system 314, is itself
operating or moving during sensing of load, pressure, or displacement.
Similarly, the capability can also correct in situation where the body,
instrument, appliance, vehicle, equipment, or other physical system, is
causing the portion 312 of the body, instrument, appliance, vehicle,
equipment, or other physical system being measured to be in motion 316
during sensing of load, force, pressure, or displacement. Other
adjustments to the measurement for physical changes to system 314 are
contemplated and can be compensated for in a similar fashion. For
example, temperature of system 314 can be measured and a lookup table or
equation having a relationship of temperature versus transit time can be
used to normalize measurements. Differential measurement techniques can
also be used to cancel many types of common factors as is known in the
art.

[0047]The use of waveguide 306 enables the construction of low cost
sensing modules and devices over a wide range of sizes, including highly
compact sensing modules, disposable modules for bio-medical applications,
and devices, using standard components and manufacturing processes. The
flexibility to construct sensing modules and devices with very high
levels of measurement accuracy, repeatability, and resolution that can
scale over a wide range of sizes enables sensing modules and devices to
the tailored to fit and collect data on the physical parameter or
parameters of interest for a wide range of medical and non-medical
applications.

[0048]For example, sensing modules or devices may be placed on or within,
or attached or affixed to or within, a wide range of physical systems
including, but not limited to instruments, appliances, vehicles,
equipments, or other physical systems as well as animal and human bodies,
for sensing the parameter or parameters of interest in real time without
disturbing the operation of the body, instrument, appliance, vehicle,
equipment, or physical system.

[0049]In addition to non-medical applications, examples of a wide range of
potential medical applications may include, but are not limited to,
implantable devices, modules within implantable devices, modules or
devices within intra-operative implants or trial inserts, modules within
inserted or ingested devices, modules within wearable devices, modules
within handheld devices, modules within instruments, appliances,
equipment, or accessories of all of these, or disposables within
implants, trial inserts, inserted or ingested devices, wearable devices,
handheld devices, instruments, appliances, equipment, or accessories to
these devices, instruments, appliances, or equipment. Many physiological
parameters within animal or human bodies may be measured including, but
not limited to, loading within individual joints, bone density, movement,
various parameters of interstitial fluids including, but not limited to,
viscosity, pressure, and localized temperature with applications
throughout the vascular, lymph, respiratory, and digestive systems, as
well as within or affecting muscles, bones, joints, and soft tissue
areas. For example, orthopedic applications may include, but are not
limited to, load bearing prosthetic components, or provisional or trial
prosthetic components for, but not limited to, surgical procedures for
knees, hips, shoulders, elbows, wrists, ankles, and spines; any other
orthopedic or musculoskeletal implant, or any combination of these.

[0050]FIG. 5 is an exemplary cross-sectional view of a sensor element 400
to illustrate changes in the propagation of ultrasound waves 414 with
changes in the length of a waveguide 406. In general, the measurement of
a parameter is achieved by relating displacement to the parameter. In one
embodiment, the displacement required over the entire measurement range
is measured in microns. For example, an external force 408 compresses
waveguide 406 thereby changing the length of waveguide 406. Sensing
circuitry (not shown) measures propagation characteristics of ultrasonic
signals in the waveguide 406 to determine the change in the length of the
waveguide 406. These changes in length change in direct proportion to the
parameters of interest thus enabling the conversion of changes in the
parameter or parameters of interest into electrical signals.

[0051]As illustrated, external force 408 compresses waveguide 406 and
pushes the transducers 402 and 404 closer to one another by a distance
410. This changes the length of waveguide 406 by distance 412 of the
waveguide propagation path between transducers 402 and 404. Depending on
the operating mode, the sensing circuitry measures the change in length
of the waveguide 406 by analyzing characteristics of the propagation of
ultrasound waves within the waveguide.

[0052]One interpretation of FIG. 5 illustrates waves emitting from
transducer 402 at one end of waveguide 406 and propagating to transducer
404 at the other end of the waveguide 406. The interpretation includes
the effect of movement of waveguide 406 and thus the velocity of waves
propagating within waveguide 406 (without changing shape or width of
individual waves) and therefore the transit time between transducers 402
and 404 at each end of the waveguide. The interpretation further includes
the opposite effect on waves propagating in the opposite direction and is
evaluated to estimate the velocity of the waveguide and remove it by
averaging the transit time of waves propagating in both directions.

[0053]Changes in the parameter or parameters of interest are measured by
measuring changes in the transit time of energy pulses or waves within
the propagating medium. Closed loop measurement of changes in the
parameter or parameters of interest is achieved by modulating the
repetition rate of energy pulses or the frequency of energy waves as a
function of the propagation characteristics of the elastic energy
propagating structure.

[0054]In a continuous wave mode of operation, a phase detector (not shown)
evaluates the frequency and changes in the frequency of resonant
ultrasonic waves in the waveguide 406. As will be described below,
positive feedback closed-loop circuit operation in continuous wave (CW)
mode adjusts the frequency of ultrasonic waves 414 in the waveguide 406
to maintain a same number or integer number of periods of ultrasonic
waves in the waveguide 406. The CW operation persists as long as the rate
of change of the length of the waveguide is not so rapid that changes of
more than a quarter wavelength occur before the frequency of the
Propagation Tuned Oscillator (PTO) can respond. This restriction
exemplifies one advantageous difference between the performance of a PTO
and a Phase Locked Loop (PLL). Assuming the transducers are producing
ultrasonic waves, for example, at 2.4 MHz, the wavelength in air,
assuming a velocity of 343 microns per microsecond, is about 143μ,
although the wavelength within a waveguide may be longer than in
unrestricted air.

[0055]In a pulse mode of operation, the phase detector measures a time of
flight (TOF) between when an ultrasonic pulse is transmitted by
transducer 402 and received at transducer 404. The time of flight
determines the length of the waveguide propagating path, and accordingly
reveals the change in length of the waveguide 406. In another
arrangement, differential time of flight measurements (or phase
differences) can be used to determine the change in length of the
waveguide 406. A pulse consists of a pulse of one or more waves. The
waves may have equal amplitude and frequency (square wave pulse) or they
may have different amplitudes, for example, decaying amplitude
(trapezoidal pulse) or some other complex waveform. The PTO is holding
the phase of the leading edge of the pulses propagating through the
waveguide constant. In pulse mode operation the PTO detects the leading
edge of the first wave of each pulse with an edge-detect receiver rather
than a zero-crossing receiver circuitry as used in CW mode.

[0056]FIG. 6 is a simplified flow chart 600 of method steps for high
precision processing and measurement data in accordance with an exemplary
embodiment. The method 600 can be practiced with more or less than the
steps shown and is not limited to the order of steps shown. The method
steps can be practiced with the aforementioned components or any other
components suitable for such processing, for example, electrical
circuitry to control the emission of energy pulses or waves and to
capture the repetition rate of the energy pulses or frequency of the
energy waves propagating through the elastic energy propagating structure
or medium.

[0057]In a step 602, the process initiates a measurement operation. In a
step 604, a known state is established by resetting digital timer 22 and
data register 26. In a step 606, digital counter 20 is preset to the
number of measurement cycles over which measurements will be taken and
collected. In a step 608, the measurement cycle is initiated and a clock
output of digital clock 24 is enabled. A clock signal from digital clock
24 is provided to both digital counter 20 and digital timer 22. An
elapsed time is counted by digital timer 20 based on the frequency of the
clock signal output by digital clock 24. In a step 610, digital timer 22
begins tracking the elapsed time at the same time that digital counter 20
starts decrementing. In one embodiment, digital counter 20 is decremented
as each energy wave propagates through waveguide 3 and detected by
transducer 6. Digital timer 20 counts down until the preset number of
measurement cycles has been completed. In a step 612, energy wave
propagation is sustained by propagation tuned oscillator as digital
counter 20 is decremented by the detection of a propagated energy wave.
In a step 614, energy wave detection, emission, and propagation continue
while the count in digital counter 20 is greater than zero. In a step
616, the clock input of digital timer 22 is disabled upon reaching a zero
count on digital counter 20 thus preventing digital counter 20 and
digital timer 22 from being clocked. In one embodiment, the preset number
of measurement cycles provided to digital counter 20 is divided by the
elapsed time measured by digital timer 22 to calculate a frequency of
propagated energy waves. Conversely, the number can be calculated as a
transit time by dividing the elapsed time from digital timer 22 by the
preset number of measurement cycles. Finally, in a step 618, the
resulting value is transferred to register 26. The number in data
register 26 can be wirelessly transmitted to a display and database. The
data from data register 26 can be correlated to a parameter being
measured. The parameter such as a force or load is applied to the
propagation medium (e.g. waveguide 3) such that parameter changes also
change the frequency or transit time calculation of the measurement. A
relationship between the material characteristics of the propagation
medium and the parameter is used with the measurement value (e.g.
frequency, transit time, phase) to calculate a parameter value.

[0058]The method 600 practiced by the example assemblage of FIG. 1, and by
way of the digital counter 20, digital timer 22, digital clock 24 and
associated electronic circuitry analyzes the digitized measurement data
according to operating point conditions. In particular, these components
accumulate multiple digitized data values to improve the level of
resolution of measurement of changes in length or other aspect of an
elastic energy propagating structure or medium that can alter the transit
time of energy pulses or waves propagating within the elastic energy
propagating structure or medium. The digitized data is summed by
controlling the digital counter 20 to run through multiple measurement
cycles, each cycle having excitation and transit phases such that there
is not lag between successive measurement cycles, and capturing the total
elapsed time. The counter is sized to count the total elapsed time of as
many measurement cycles as required to achieve the required resolution
without overflowing its accumulation capacity and without compromising
the resolution of the least significant bit of the counter. The digitized
measurement of the total elapsed transit time is subsequently divided by
the number of measurement cycles to estimate the time of the individual
measurement cycles and thus the transit time of individual cycles of
excitation, propagation through the elastic energy propagating structure
or medium, and detection of energy pulses or waves. Accurate estimates of
changes in the transit time of the energy pulses or waves through the
elastic energy propagating structure or medium are captured as elapsed
times for excitation and detection of the energy pulses or waves are
fixed.

[0059]Summing individual measurements before dividing to estimate the
average measurement value data values produces superior results to
averaging the same number of samples. The resolution of count data
collected from a digital counter is limited by the resolution of the
least-significant-bit in the counter. Capturing a series of counts and
averaging them does not produce greater precision than this
least-significant-bit, that is the precision of a single count. Averaging
does reduce the randomness of the final estimate if there is random
variation between individual measurements. Summing the counts of a large
number of measurement cycles to obtain a cumulative count then
calculating the average over the entire measurement period improves the
precision of the measurement by interpolating the component of the
measurement that is less than the least significant bit of the counter.
The precision gained by this procedure is on the order of the resolution
of the least-significant-bit of the counter divided by the number of
measurement cycles summed.

[0060]The size of the digital counter and the number of measurement cycles
accumulated may be greater than the required level of resolution. This
not only assures performance that achieves the level of resolution
required, but also averages random component within individual counts
producing highly repeatable measurements that reliably meet the required
level of resolution.

[0061]The number of measurement cycles is greater than the required level
of resolution. This not only assures performance that achieves the level
of resolution required, but also averages any random component within
individual counts producing highly repeatable measurements that reliably
meet the required level of resolution.

[0062]FIG. 7 is an illustration of a sensor 700 placed in contact between
a femur 702 and a tibia 708 for measuring a parameter in accordance with
an exemplary embodiment. In general, the sensor 700 is placed in contact
with or in proximity to the muscular-skeletal system to measure a
parameter. In a non-limiting example, sensor 700 can be operated in
continuous wave mode, pulse mode, and pulse echo-mode to measure a
parameter of a joint or an artificial joint. Embodiments of sensor 700
are broadly directed to measurement of physical parameters, and more
particularly, to evaluating changes in the transit time of a pulsed
energy wave propagating through a medium. In-situ measurements during
orthopedic joint implant surgery would be of substantial benefit to
verify an implant is in balance and under appropriate loading or tension.
In one embodiment, the instrument is similar to and operates familiarly
with other instruments currently used by surgeons. This will increase
acceptance and reduce the adoption cycle for a new technology. The
measurements will allow the surgeon to ensure that the implanted
components are installed within predetermined ranges that maximize the
working life of the joint prosthesis and reduce costly revisions.
Providing quantitative measurement and assessment of the procedure using
real-time data will produce results that are more consistent. A further
issue is that there is little or no implant data generated from the
implant surgery, post-operatively, and long term. Sensor 700 can provide
implant status data to the orthopedic manufacturers and surgeons.
Moreover, data generated by direct measurement of the implanted joint
itself would greatly improve the knowledge of implanted joint operation
and joint wear thereby leading to improved design and materials.

[0063]In at least one exemplary embodiment, an energy pulse is directed
within one or more waveguides in sensor 700 by way of pulse mode
operations and pulse shaping. The waveguide is a conduit that directs the
energy pulse in a predetermined direction. The energy pulse is typically
confined within the waveguide. In one embodiment, the waveguide comprises
a polymer material. For example, urethane or polyethylene are polymers
suitable for forming a waveguide. The polymer waveguide can be compressed
and has little or no hysteresis in the system. Alternatively, the energy
pulse can be directed through the muscular-skeletal system. In one
embodiment, the energy pulse is directed through bone of the
muscular-skeletal system to measure bone density. A transit time of an
energy pulse is related to the material properties of a medium through
which it traverses. This relationship is used to generate accurate
measurements of parameters such as distance, weight, strain, pressure,
wear, vibration, viscosity, and density to name but a few.

[0064]Sensor 700 can be size constrained by form factor requirements of
fitting within a region the muscular-skeletal system or a component such
as a tool, equipment, or artificial joint. In a non-limiting example,
sensor 700 is used to measure load and balance of an installed artificial
knee joint. A knee prosthesis comprises a femoral prosthetic component
704, an insert, and a tibial prosthetic component 706. A distal end of
femur 702 is prepared and receives femoral prosthetic component 704.
Femoral prosthetic component 704 typically has two condyle surfaces that
mimic a natural femur. As shown, femoral prosthetic component 704 has
single condyle surface being coupled to femur 702. Femoral prosthetic
component 704 is typically made of a metal or metal alloy.

[0065]A proximal end of femur 708 is prepared to receive tibial prosthetic
component 706. Tibial prosthetic component 706 is a support structure
that is fastened to the proximal end of the tibia and is usually made of
a metal or metal alloy. The tibial prosthetic component 706 also retains
the insert in a fixed position with respect to femur 708. The insert is
fitted between femoral prosthetic component 704 and tibial prosthetic
component 706. The insert has at least one bearing surface that is in
contact with at least condyle surface of femoral prosthetic component
704. The condyle surface can move in relation to the bearing surface of
the insert such that the lower leg can rotate under load. The insert is
typically made of a high wear plastic material that minimizes friction.

[0066]In a knee joint replacement process, the surgeon affixes femoral
prosthetic component 704 to the femur 702 and tibial prosthetic component
706 to femur 708. The tibial prosthetic component 706 can include a tray
or plate affixed to the planarized proximal end of the femur 708. Sensor
700 is placed between a condyle surface of femoral prosthetic component
704 and a major surface of tibial prosthetic component 706. The condyle
surface contacts a major surface of sensor 700. The major surface of
sensor 700 approximates a surface of the insert. Tibial prosthetic
component 706 can include a cavity or tray on the major surface that
receives and retains sensor 700 during a measurement process. Tibial
prosthetic component 706 and sensor 700 has a combined thickness that
represents a combined thickness of tibial prosthetic component 706 and a
final (or chronic) insert of the knee joint.

[0067]In one embodiment, two sensors 700 are fitted into two separate
cavities, the cavities are within a trial insert (that may also be
referred to as the tibial insert, rather than the tibial component
itself) that is held in position by tibial component 706. One or two
sensors 700 may be inserted between femoral prosthetic component 704 and
tibial prosthetic component 706. Each sensor is independent and each
measures a respective condyle of femur 702. Separate sensors also
accommodate a situation where a single condyle is repaired and only a
single sensor is used. Alternatively, the electronics can be shared
between two sensors to lower cost and complexity of the system. The
shared electronics can multiplex between each sensor module to take
measurements when appropriate. Measurements taken by sensor 700 aid the
surgeon in modifying the absolute loading on each condyle and the balance
between condyles. Although shown for a knee implant, sensor 700 can be
used to measure other orthopedic joints such as the spine, hip, shoulder,
elbow, ankle, wrist, interphalangeal joint, metatarsophalangeal joint,
metacarpophalangeal joints, and others. Alternatively, sensor 700 can
also be adapted to orthopedic tools to provide measurements.

[0068]The prosthesis incorporating sensor 700 emulates the function of a
natural knee joint. Sensor 700 can measure loads or other parameters at
various points throughout the range of motion. Data from sensor 700 is
transmitted to a receiving station 710 via wired or wireless
communications. In a first embodiment, sensor 700 is a disposable system.
Sensor 700 can be disposed of after using sensor 700 to optimally fit the
joint implant. Sensor 700 is a low cost disposable system that reduces
capital costs, operating costs, facilitates rapid adoption of
quantitative measurement, and initiates evidentiary based orthopedic
medicine. In a second embodiment, a methodology can be put in place to
clean and sterilize sensor 700 for reuse. In a third embodiment, sensor
700 can be incorporated in a tool instead of being a component of the
replacement joint. The tool can be disposable or be cleaned and
sterilized for reuse. In a fourth embodiment, sensor 700 can be a
permanent component of the replacement joint. Sensor 700 can be used to
provide both short term and long term post-operative data on the
implanted joint. In a fifth embodiment, sensor 700 can be coupled to the
muscular-skeletal system. In all of the embodiments, receiving station
710 can include data processing, storage, or display, or combination
thereof and provide real time graphical representation of the level and
distribution of the load. Receiving station 710 can record and provide
accounting information of sensor 700 to an appropriate authority.

[0069]In an intra-operative example, sensor 700 can measure forces (Fx,
Fy, Fz) with corresponding locations and torques (e.g. Tx, Ty, and Tz) on
the femoral prosthetic component 704 and the tibial prosthetic component
706. The measured force and torque data is transmitted to receiving
station 710 to provide real-time visualization for assisting the surgeon
in identifying any adjustments needed to achieve optimal joint pressure
and balancing. The data has substantial value in determining ranges of
load and alignment tolerances required to minimize rework and maximize
patient function and longevity of the joint.

[0070]As mentioned previously, sensor 700 can be used for other joint
surgeries; it is not limited to knee replacement implant or implants.
Moreover, sensor 700 is not limited to trial measurements. Sensor 700 can
be incorporated into the final joint system to provide data
post-operatively to determine if the implanted joint is functioning
correctly. Early determination of a problem using sensor 700 can reduce
catastrophic failure of the joint by bringing awareness to a problem that
the patient cannot detect. The problem can often be rectified with a
minimal invasive procedure at lower cost and stress to the patient.
Similarly, longer term monitoring of the joint can determine wear or
misalignment that if detected early can be adjusted for optimal life or
replacement of a wear surface with minimal surgery thereby extending the
life of the implant. In general, sensor 700 can be shaped such that it
can be placed or engaged or affixed to or within load bearing surfaces
used in many orthopedic applications (or used in any orthopedic
application) related to the musculoskeletal system, joints, and tools
associated therewith. Sensor 700 can provide information on a combination
of one or more performance parameters of interest such as wear, stress,
kinematics, kinetics, fixation strength, ligament balance, anatomical fit
and balance.

[0071]The present invention is applicable to a wide range of medical and
nonmedical applications including, but not limited to, frequency
compensation; control of, or alarms for, physical systems; or monitoring
or measuring physical parameters of interest. The level of accuracy and
repeatability attainable in a highly compact sensing module or device may
be applicable to many medical applications monitoring or measuring
physiological parameters throughout the human body including, not limited
to, bone density, movement, viscosity, and pressure of various fluids,
localized temperature, etc. with applications in the vascular, lymph,
respiratory, digestive system, muscles, bones, and joints, other soft
tissue areas, and interstitial fluids.

[0072]While the present invention has been described with reference to
particular embodiments, those skilled in the art will recognize that many
changes may be made thereto without departing from the spirit and scope
of the present invention. Each of these embodiments and obvious
variations thereof is contemplated as falling within the spirit and scope
of the invention.